Hot-gas reciprocating engine

ABSTRACT

A hot-gas reciprocating engine in which at least the part of the cylinder which bounds the hot expansion space and at least the regenerator housing part which encloses the regenerator part of higher temperature have inner walls which are provided with a heat-insulating layer; cooling members maintain these parts of cylinder and regenerator housing at a lower temperature.

United States Patent [191 Lynch et al.

[ Jan. 21, 1975 HOT-GAS RECIPROCATING ENGINE [75] Inventors: BrianLynch; Roeli Jan Meijer, both of Emmasingel, Eindhoven, Netherlands [73]Assignee: U.S. Philips Corporation, New

York, N.Y.

[22] Filed: Dec. 12, 1973 [21] Appl. No.: 424,114

[30] Foreign Application Priority Data Jan. 2, 1973 Netherlands 7300002[52] US. Cl. 60/524, 60/526 [51] Int. Cl. F02g 1/04 [58] Field of Search60/516, 517, 524, 526

[56] References Cited UNITED STATES PATENTS Meijer et al. 60/524 FOREIGNPATENTS OR APPLICATIONS 87,805 4/1958 Netherlands 60/524 PrimaryExaminerMartin P. Schwadron Assistant Examiner-Allen M. OstragerAttorney, Agent, or Firm-Frank R. Trifari [5 7] ABSTRACT A hot-gasreciprocating engine in which at least the 7 part of the cylinder whichbounds the hot expansion space and at least the regenerator housing partwhich encloses the regenerator part of higher temperature have innerwalls which are provided with a heatinsulating layer; cooling membersmaintain these parts of cylinder and regenerator housing at a lowertemperature.

9 Claims, 4 Drawing Figures PATENIED JAN 21 I975 SHEET 2 BF 4 HOT-GASRECIPROCATING ENGINE BACKGROUND OF THE INVENTION The invention relatesto a known type of hot-gas reciprocating engine, comprising at least onecylinder with an expansion space of variable volume and higher meantemperature during operation, the said expansion space communicating,via a regenerator which is incorporated in a housing, with a compressionspace of variable volume and of lower mean temperature during operation.The compression and expansion spaces which together constitute a workingspace can be present in the same cylinder (British patent specificationsNos. 857,758 and 898,270) or in two different cylinders (British patentspecifications Nos. 695,014 and 708,199). 1

During operation of such a hot-gas reciprocating engine, heat is appliedto the working medium in the engine, for example, helium or hydrogen,via a heat exchanger: the heater which usually consists of a number ofpipes. A medium, such as the combustion gases which flow along thepipes, gives off heat through the pipe walls to the working mediumflowing through these pipes.

In the efforts to achieve a higher specific power (shaft horse power perlitre of cylinder capacity) by increasing the working medium pressure inthe engine and to increase the thermal efficiency by increasing theheater temperature, a problem is encountered in that the commonly usedand comparatively inexpensive construction materials for cylinders andregenerator housings can no longer be used.

For example, the commonly used stainless steel types have an intolerablecreepage rate at working medium pressures in excess of approximately 100atmospheres absolute and temperatures in excess of approximately 650C.High-quality metal alloys can be used which are capable of withstandinghigh working medium pressures and temperatures, however, a majordrawback is that these metal alloys contain rather rare elements such ascobalt and nickel, which is one of the main reasons, if not the majorreason, why they are expensive. The high cost of these metal alloys andthe dependency on rather rare metals make the application of such alloysunattractive in the bulk manufacture of hot-gas reciprocating engines.In addition, alloys of this kind can be less readily machined thanmaterials such as stainless steel.

SUMMARY OF THE INVENTION The present invention has for its object tomitigate these drawbacks by providing a hot-gas reciprocating enginewhich can be operated at high working medium pressures (up toapproximately 250 ata) and at high heater temperatures, withoutexpensive construction materials which contain rare metals and which aredifficult to machine being required for cylinders and regeneratorhousings.

So as to achieve this object, the ht-gas reciprocating engine accordingto the invention is characterized in that at least the part of thecylinder which bounds the expansion space and at least the part of theregenerator housing which envelops the regenerator part of highertemperature during operation facing the expansion space, have innerwalls which are each provided with at least one layer of aheat-insulating material; this layer acts as a partition between thecylinder part and the expansion space and between the regeneratorhousing part and the regenerator part, respectively, cooling membersbeing provided for maintaining a lower mean temperature of the saidparts of cylinder and regenerator housing during operationv Due to theprovision of the heat-insulating layer on the inner walls of cylinderand regenerator housing, the cylinder and the housing are no longer indirect thermal and mechanical contact with the working medium. At hightemperatures and high pressures of the working medium, the thermal andthe mechanical loading of the cylinder wall and the regenerator housingwall then remain low. The cylinders and regeneratorhousings of suchhigh-load hot-gas reciprocating engines can thus be manufactured ofconventional, inexpensive construction materials such as nodular castiron or lowalloy steel types which can also be readily machined.

The cooling members ensure that a high temperature gradient in theradial direction across the heat-.

insulating layer is maintained under all circumstances. Temperatureequalization in the radial direction after a given period of operation,which might cause an excessively high temperature level of cylinder andregenerator housing, is thus prevented. The quantity of heat to bedischarged from the cylinders and regenerator housings remains limiteddue to the heat-insulating layer, with the result that the thermalefficiency of the engine is high. If the heat-insulating layer were notprovided, the cooling would cause a catastrophical loss of thermalefficiency.

In a preferred embodiment of the hot-gas reciprocating engine accordingto the invention, the heatinsulating layer is made of a ceramicmaterial. Notably given glass ceramic materials offer the advantage thatthey have a very low heat conductivity and expansion coefficient,favourable thermal impact resistance and proper mechanical strength.

The low heat conductivity coefficient makes it possible to maintain, inthe case of a small wall thickness of the heat-insulating layer (forexample, 5 mm) and a comparatively low cooling capacity, comparativelylow temperatures (for example C) at the area of the interface betweenthe heat-insulating layer and the cylinder or the regenerator housing,respectively. The low expansion coefficient ensures that there is norisk of chipping of the glass ceramic material in the case of workingmedium temperature fluctuations. The favorable thermal shock-resistancemakes it possible to maintain a very steep temperature gradientpermanently over a very thin glass ceramic layer. The favorablemechanical strength, finally, renders the heatinsulating layer capableof withstanding the variable mechanical loads which are caused by thevariable working medium pressures in the engine. The heatinsulatingglass ceramic layer can be deposited directly on the inner wall ofcylinder and regenerator housing. It is alternatively possible to makeuse of glass ceramic jackets as inserts which are fastened afterinsertion in the cylinder and regenerator housing.

A preferred embodiment of the hot-gas reciprocating engine according tothe invention is characterized in that the part of the cylinder whichbounds the expansion space and the part of the regenerator housing whichenvelops the regenerator part of higher temperature which faces theexpansion space are enveloped by a heat pipe which serves as a coolingmember. This heat pipe contains a heat transport medium which completesan evaporation-condensation cycle during operation, evaporation takingplace by taking up heat from the cylinder or the regenerator housing,respectively, and condensation taking place elsewhere on aheattransmitting heat pipe wall while giving off heat thereto.

A heat pipe is to be understood to mean herein a heat transport devicewhich is formed by a reservoir in which a small quantity of heattransport medium, for example water, is present which, on the one side,evaporates from a wall by taking up heat from a heat source and which,on the other side, gives off heat to another wall while changing overfrom the vapor to the liquid phase.

Using a heat pipe of this kind, very large quantities of heat can betransported without a pumping device or other moving parts beingrequired. Condensed heat transport medium can be returned to the wallwhere evaporation takes place under the influence of gravity. However,the heat pipe often comprises a capillary structure which connects thecondensation wall to the evaporation wall and through which condensateis returned under all circumstances to the evaporation wall by capillaryaction.

Heat pipes provided with a capillary structure for returning condensateare known per se, for example, from United States patent specificationNos. 3,299,795 and 3,402,767. 767. The heat pipe can serve as aconverter from high to low heat flow density in that the heat taken upfrom the cylinder or regenerator housing wall as the evaporation wallcan be spread over a heat pipe condensation wall of larger surface area.

In a further preferred embodiment of the hot-gas reciprocating engineaccording to the invention, the said parts of cylinder and regeneratorhousing are provided with a cooling jacket which comprises one or moreducts through which cooling liquid can flow. According to the invention,it is advantageous to incorporate one or both cooling jackets in aclosed duct system in which the cooling liquid can circulate, the saidduct system elsewhere containing a heat exchanger in which the liquidcan give off heat to the surroundings.

If a hot-gas engine of this kind is used as a traction engine, it can atthe same time provide the heating of the passenger compartment. In theknown hot-gas engine comprising a cooler for discharging the compressionheat of the working medium, the cooling water temperature is normallytoo low for realizing proper heating of the passenger compartment.

The invention will be described in detail hereinafter with reference tothe drawing in which a few embodiments of the hot-gas reciprocatingengine are diagrammatically shown (not to scale) by way of example.

BRIEF DESCRIPTION OF THE DRAWINGS F IG. 1 is a longitudinal sectionalview of a hot-gas reciprocating engine,

FIG. 2 is a plan view of a 4-cylinder double-acting hot-gasreciprocating engine,

FIG. 3 is a sectional view taken along the line IIIIII of FIG. 2, and

FIG. 4 is a longitudinal sectional view of an indirectly heated hot-gasreciprocating engine.

DESCRIPTION OF THE PREFERRED EMBODIMENT The reference numeral 1 in FIG.1 denotes a cylinder in which a piston 2 and a displacer 3 can move at aphase difference. The piston and the displacer are connected to a drivesystem not shown, by means of a piston rod 4 and a displacer rod 5,respectively. Present between the piston 2 and the displacer 3 is acompression space 6 which is in open communication with an expansionspace 10 above the displacer via a coller 7 for discharging thecompression heat, a regenerator 8 and a heater 9.

The heater 9 consists of a plurality of bent pipes which are arranged ina ring about the space 11 for combustion gases and which eachcommunicate on the one side with regenerator 8 and on the other sidewith expansion space 10. The arrangement is such that an inner pipe row9 and an outer pipe row 9" are provided, the latter row being concentricwith the former. Present between the pipes of each row are gaps whichserve as passages for combustion gases. The pipes of outer row 9' areprovided on their lower ends with fins 12 so as to increase theheat-transfer surface at this area. The hot-gas reciprocating enginecomprises a burner device 13 with a burner 14 and an inlet 15 forcombustion air. Also provided is an outlet 16 for combustion gases.

During operation of the hot-gas engine, the hot combustion gases(temperature, for example, 2,200C) originating from the burner device 13flow along the pipes of the inner row 9' while giving off heat thereto,subsequently along the pipes of the outer row 9" while giving off heatthereto and after that, after having given off heat also to fins 12,they leave the engine via outlet 16.

The inner wall of the upper higher temperature part of cylinder 1 isprovided with a heat-insulating layer of a glass ceramic material 17.Arranged about this cylinder part is a cooling jacket 18 comprisingcooling ducts 19 through which a cooling liquid can flow.

Cooling jacket 18 is thermally shielded from the combustion gas space 1l by heat-insulating material 20 and shield 21. By a suitable choice ofthe thermal leakage of the heat-insulating material, additional heatwhich originates from the combustion gases can be given off to thecooling liquid so that a higher cooling liquid temperature (for heatingpurposes) is achieved.

Regenerator 8 is accommodated in a housing 22, the inner wall of whichis also provided with a layer of heatinsulating glass ceramic material,denoted by the reference numeral 23. A cooling jacket 24 comprisingcooling ducts 25 is arranged about housing 22. The glass ceramic layers17 and 23 shield the cooled cylinder wall and the cooled regeneratorhousing wall, respectively, from hot working medium under high pressure.Consequently, the operating temperature of cylinder 1 and regeneratorhousing 22 is low so that conventional materials can be used. Thecooling jackets l8 and 24 ensure that the steep temperature gradientover the layers 17 and 23, viewed in the radial direction, is maintainedand that no temperature equalization occurs in this direction in thecourse of time.

The hot-gas engine of FIG. 2 comprises four cylinders, 31, 32, 33 and34, for four thermodynamic cycles. The regenerator and cooler associatedwith a given cycle are both situated in a common space, i.e., in thespaces 35, 36, 37 and 38, respectively. The four cylinders as well asthe spaces for regenerator and cooler are arranged in a ring. Present inthe space 37 of FIG. 3 is a regenerator 39 and a cooler 40. The spaces35, 36

and 38 also accommodate a regenerator and a cooler which are not shownin the Figure.

The piston 41 reciprocates in cylinder 33. Present above the piston isan expansion space 42 which communicates with heater pipes 43, the otherends of which open into a duct 44. Present below piston 41 is acompression space 45 which communicates with a duct 46. Regenerator 39has connected thereto heater pipes 47, the other end of which opens intoduct 44. A duct 48 communicates with cooler 40.

In a double-acting engine, the expansion space of one cylindercommunicates, via a heater, regenerator and cooler, with the compressionspace of another cylinder, the expansion space of said other cylindercommunicating, again via a heater, regenerator and cooler, with thecompression space of a next cylinder.

In the present case, expansion space 42 in cylinder 33 is in opencommunication, via heater pipes 43, duct 44, heater pipes 47,regenerator 39, cooler 40 and duct 48, with the compression space (notshown) in cylinder 34. Compression space 45 in cylinder 33 communicates,via duct 46, the cooler and regenerator (not shown) in space 36, andheater pipes (not shown), with the expansion space (not shown) incylinder 32.

The heater pipes associated with the four thermodynamic cycles arearranged in a ring about a space 50 for combustion gases. The hotcombustion gases originate from one central burner device 51, providedwith an inlet for combustion air 52 and an inlet for fuel 53. An outlet54 for combustion gases communicates with space 50. The inner walls ofthe cylinders 31 to 34 are covered with a layer of glass ceramicmaterial, denoted by the reference numeral 55 for cylinder 33 in FIG. 3.Arranged about each cylinder is a cooling jacket 56 comprising an inletand an outlet, 57 and 58, respectively, for cooling liquid.

At the area where they form the regenerator housing, the inner walls ofspaces 35, 36, 37 and 38 (FIG. 2) are also covered with a layer of glassceramic material 59. Provided about each of the regenerator housings isa cooling jacket 60 comprising an inlet and an outlet, 61 and 62,respectively, for cooling liquid.

The hot-gas reciprocating engine shown in FIG. 4 comprises two cylinders70 and 71. Present in cylinder 70 is a displacer 72 which is providedwith a heatinsulating displacer cap 73 of glass ceramic material. Viadisplacer rod 74, displacer 72 is connected to a crank shaft 75. Presentin cylinder 71 is a piston 76 which is connected to crank shaft 75 viapiston rod 77. Present above displacer 72 is the expansion space 78 86to the heat-transmitting wall 84 where it evaporates again. The part ofcylinder 70 which bounds expansion space 78 is again covered on theinner side with a layer of heat-insulating glass ceramic material,denoted by the reference 87. Similarly, the upper part of cylinder. 71,forming the housing for regenerator 80, is provided.

heat from these cylinder parts and the water vapour which communicates,via heater pipes 79, regenerator 80 and cooler 81, with compressionspace 82 above piston 76.

Heater pipes 79 are situated inside a heat pipe 83 which has aheat-transmitting wall 84 and which for the remainder is thermallyinsulated from the surroundings by means of a heat-insulating jacket 85.The inner wall of heat pipe 83 is covered with a capillary structure 86which is formed, for example, by a gauze layer. Furthermore, the heatpipe 83 contains a quantity of sodium as the heat transport medium.

During operation, heat is given off to the sodium in the heat pipe viaheattransmitting wall 84, with the result that the sodium evaporates.Sodium vapor subsequently flows to the heater pipes 79 and condensesthereon while giving off heat. Sodium condensate is returned bycapillary action through capillary structure formed condenses onheat-transmitting wall 92 while giving off heat through this wall to thesurroundings.

What is claimed is: 1. A hot-gas reciprocating engine, comprising atleast one cylinder with an expansion space of variable volume and highermean temperature during operation,

the said expansion space communicating, via a regenerator which isincorporated in a housing, with a compression space of variable volumeand lower mean temperature during operation, characterized in that atleast the part of the cylinder which bounds the expansion space and atleast the part of the regenerator housing which envelops the regeneratorpart of higher temperature during operation facing the expansion spacehave inner walls which are each provided with at least one layer of aheat-insulating material which acts as a partition between the cylinderpart and the expansion space and between the regenerator housing partand the regenerator part, respectively, cooling members being providedfor maintaining a lower mean temperature of the said parts of cylinderand regenerator housing during operation.

2. A hot-gas reciprocating engine as claimed in claim 1, characterizedin that the heat-insulating layer is made of a ceramic material,particularly a glass ceramic material.

3. a hot-gas reciprocating engine as claimed in claim 1, characterizedin that the said parts of cylinder and regenerator housing are envelopedby a heat pipe as a cooling member, the said heat pipe containing a heattransport medium which completes an evaporationcondensation cycle duringoperation, evaporating taking place by taking up heat from the cylinderor the regenerator housing, whilst condensation takes place elsewhere ona heat-transmitting heat pipe wall while giving off heat to this wall.

4. A hot-gas reciprocating engine as claimed in claim 1, characterizedin that the said parts of cylinder and regenerator housing are providedwith a cooling jacket which comprises one or more ducts through which acooling liquid can flow.

5. A hot-gas reciprocating engine as claimed in claim 4, characterizedin that one or both cooling jackets are incorporated in a closed ductsystem in which the cooling liquid can circulate, the said duct systemelsewhere comprising a heat exchanger in which the liquid can give offheat to the surroundings.

6. In a hot gas engine including a housing whose walls define variablevolume expansion and compression cooling means for maintaining a meantemperature ofsaid first and second wall parts during operation of saidapparatus lower than said higher mean temperature of said expansionspace, whereby conventional materials may be used for said housing firstand second wall parts.

7. Apparatus according to claim 6 wherein said heat insulating layercomprises a ceramic material such as glass. 7

8. Apparatus according to claim 6 wherein said first and second wallparts comprise heat pipes, each heat pipe containing a heat transportmedium which completes an evaporation-condensation cycle duringoperation, with evaporation occurring when heat is transferred from saidexpansion space or regenerator to said heat pipe and condensation occurswhen heat is transferred from said heat pipe outward thereof.

9. Apparatus according to claim 6 and operable with a source of coolingliquid, wherein said first and second wall parts comprise ductstherethrough, said apparatus further comprising means for flowing saidcooling liquid through said ducts to cool said wall parts.

1. A hot-gas reciprocating engine, comprising at least one cylinder withan expansion space of variable volume and higher mean temperature duringoperation, the said expansion space communicating, via a regeneratorwhich is incorporated in a housing, with a compression space of variablevolume and lower mean temperature during operation, characterized inthat at least the part of the cylinder which bounds the expansion spaceand at least the part of the regenerator housing which envelops theregenerator part of higher temperature during operation facing theexpansion space have inner walls which are each provided with at leastone layer of a heat-insulating material which acts as a partitionbetween the cylinder part and the expansion space and between theregenerator housing part and the regenerator part, respectively, coolingmembers being provided for maintaining a lower mean temperature of thesaid parts of cylinder and regenerator housing during operation.
 2. Ahot-gas reciprocating engine as claimed in claim 1, characterized inthat the heat-insulating layer is made of a ceramic material,particuLarly a glass ceramic material.
 3. a hot-gas reciprocating engineas claimed in claim 1, characterized in that the said parts of cylinderand regenerator housing are enveloped by a heat pipe as a coolingmember, the said heat pipe containing a heat transport medium whichcompletes an evaporation-condensation cycle during operation,evaporating taking place by taking up heat from the cylinder or theregenerator housing, whilst condensation takes place elsewhere on aheat-transmitting heat pipe wall while giving off heat to this wall. 4.A hot-gas reciprocating engine as claimed in claim 1, characterized inthat the said parts of cylinder and regenerator housing are providedwith a cooling jacket which comprises one or more ducts through which acooling liquid can flow.
 5. A hot-gas reciprocating engine as claimed inclaim 4, characterized in that one or both cooling jackets areincorporated in a closed duct system in which the cooling liquid cancirculate, the said duct system elsewhere comprising a heat exchanger inwhich the liquid can give off heat to the surroundings.
 6. In a hot gasengine including a housing whose walls define variable volume expansionand compression spaces of higher and lower mean temperaturesrespectively during operation, and a regenerator through which saidexpansion and compression spaces communicate, said walls comprising afirst part whose inside surfaces bound said expansion space and secondpart whose inside surfaces envelop said regenerator, the improvement incombination therewith comprising a layer of heat insulating material onsaid inside wall surfaces of at least said first and second wall parts,and cooling means for maintaining a mean temperature of said first andsecond wall parts during operation of said apparatus lower than saidhigher mean temperature of said expansion space, whereby conventionalmaterials may be used for said housing first and second wall parts. 7.Apparatus according to claim 6 wherein said heat insulating layercomprises a ceramic material such as glass.
 8. Apparatus according toclaim 6 wherein said first and second wall parts comprise heat pipes,each heat pipe containing a heat transport medium which completes anevaporation-condensation cycle during operation, with evaporationoccurring when heat is transferred from said expansion space orregenerator to said heat pipe and condensation occurs when heat istransferred from said heat pipe outward thereof.
 9. Apparatus accordingto claim 6 and operable with a source of cooling liquid, wherein saidfirst and second wall parts comprise ducts therethrough, said apparatusfurther comprising means for flowing said cooling liquid through saidducts to cool said wall parts.